Turbine efficiency tailoring

ABSTRACT

A turbomachinery apparatus. A turbine is provided with a retainer having a bore step element for turbine wheel retention, and with an aperture manifesting a tailored diameter less than the trim diameter of the turbine, thereby to permit customization of the turbine efficiency characteristic. Various configurations of turbine retainers, with tailored diameter apertures, are disclosed.

BACKGROUND OF THE INVENTION

1. Field of the Invention (Technical Field)

The present invention relates generally to turbomachinery, particularlyturbocharged internal combustion engines, and specifically relates to aturbine housing for improving the turbine efficiency characteristic.

2. Background Art

It is known in the general art of internal combustion engines to providesome system of turbocharging, whereby a turbine harnesses energy fromexhaust gases to power a compressor. The compressor is then used toincrease engine performance, typically by boosting the pressure of airsupplied to the engine.

Nearly as important as engine performance is the need for cleanerexhausts. Most internal combustion engines are subject to regulationsgoverning pollutant levels in engine emissions. “Stationary sources”such as internal combustion engine powered generators and the like, aswell as motor vehicles, are required to maintain emissions of certainpollutants, such as CO and NO_(X), below legal limits. Pollutioncontrol, however, ideally is accomplished while compromising engineperformance as little as possible.

One mode of reducing the emissions of internal combustionengines—regardless of whether the engine is turbocharged, but frequentlywhen it is—is through exhaust gas recirculation (EGR). EGR involves thereturn to the engine's intake manifold of some portion of the engineexhaust. Exhaust gases are diverted from the exhaust manifold through aduct or conduit for delivery to the intake manifold, thereby allowingexhaust to be introduced to the combustion cycle, so that oxygen contentis reduced, which in turn reduces the high combustion temperature thatcontributes to excessive NO_(X) formation.

With the introduction of EGR systems on, for example, heavy-duty dieselengines, the desired turbine efficiency characteristic does not conformto conventional turbomachinery performance. Simply accepting classicalturbomachinery turbine efficiency characteristic when using applicants'VNT™ brand of variable nozzle turbine turbocharger EGR System causesseveral effects, including: (1) Unacceptably high fuel consumption atcertain engine operating speeds; (2) Unacceptably high turbochargerspeed (i.e., turbocharger speeds which exceed acceptable limits usingknown production materials and processes); and (3) An inability to drivethe EGR at all desires engine operating points.

Further, with the use of EGR systems in use on a heavy-duty dieselengine, the turbocharger “match” to the engine results in unusualturbocharger turbine wheel matching. In some instances, for example, thetraditional or conventional wheel contour is removed from the design.This unusual machining of the turbine wheel may result in an increaseddifficulty in retaining the turbine wheel in the event the turbine wheelseparates from the turbocharger shaft. In such an event, the turbinewheel will exit the turbine housing gas outlet at a substantially highervelocity and energy than in a similar circumstance with currentturbocharger assembly designs.

Against the foregoing background, the present invention was developed.The turbine housing is modified to retain the wheel and to tailor theturbocharger turbine efficiency, thus addressing the deficiencies notedabove. The scope of applicability of the present invention will be setforth in part in the detailed description to follow, taken inconjunction with the accompanying drawings, and in part will becomeapparent to those skilled in the art upon examination of the following,or may be learned by practice of the invention. The objects andadvantages of the invention may be realized and attained by means of theinstrumentalities and combinations particularly pointed out in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated into and form a partof the specification, illustrate two embodiments of the presentinvention and, together with the description, serve to explain theprinciples of the invention. The drawings are only for the purpose ofillustrating a preferred embodiment of the invention and are not to beconstrued as limiting the invention. In the drawings:

FIG. 1 is a side (axial) sectional view of one embodiment of the turbineapparatus according to the present invention;

FIG. 2A is a side (axial) sectional view of a retainer ring element ofthe apparatus depicted in FIG. 1;

FIG. 2B is an end view of the retainer ring element seen in FIG. 2A;

FIG. 3 is a side sectional view of another embodiment of the apparatusaccording to the present invention, showing a retainer ring integrallycast with the turbine housing;

FIG. 4 is a side sectional view of another embodiment of the apparatusaccording to the present invention, showing a removably insertableretainer ring;

FIG. 5 is a side sectional view of another alternative embodiment of thepresent invention, showing a retainer ring that is movable axiallywithin the housing and securable at differing positions;

FIG. 6 is a side sectional view of yet another alternative embodiment ofthe present invention showing a retainer ring that is integrally castwith the turbine housing, and having aerodynamic protrusions extendingradially inward;

FIG. 6A is an end (radial) sectional view of the apparatus seen in FIG.6, the section taken along line A—A in FIG. 6;

FIG. 7 is a side sectional view of yet another alternative embodiment ofthe present invention showing a retainer ring that is integrally castwith the turbine housing, and having rectilinear protrusions extendingradially inward;

FIG. 7A is an end (radial) sectional view of the apparatus seen in FIG.7, the section taken along line A—A in FIG. 7;

FIG. 8 is a side sectional view of yet another alternative embodiment ofthe apparatus of the present invention, showing a retainer ring that isadjustable in radial diameter as well as having a selectively adjustableaxial position within the turbine housing;

FIG. 8A is an end (radial) sectional view of the apparatus seen in FIG.8, the section taken along line A—A in FIG. 8; and

FIG. 9 is a graph depicting relative impact of sizing of a fixedconfiguration tailored diameter, according to the present invention,with respect to a fixed trim diameter in terms of turbine pressure ratioand turbine efficiency.

DESCRIPTION OF THE PREFERRED EMBODIMENTS (BEST MODES FOR CARRYING OUTTHE INVENTION)

The present invention relates to turbines, particularly but notnecessarily turbines used in turbocharged engines. The apparatus of theinvention may find beneficial use in connection with Exhaust GasRecirculation (EGR) systems used with diesel-fueled power plants,including but not limited to the engines of large motor vehicles. Bymodifying according to this invention the turbine wheel retainmentdesign, the turbine efficiency characteristic can be tailored to meetspecialized needs, and turbine wheel retention is promoted. Accordingly,the present invention ameliorates wheel retention and turbine efficiencycharacteristic problems attributable to the use of EGR systems inconjunction with turbines. The problems are addressed with inventivemodification of the turbine housing. The present invention, as furthercharacterized and disclosed hereafter, includes such modifications.

As known in the art, a turbine work is directly proportional to turbineefficiency, mass flow, ratio of pressure across the turbine and inlettemperature. Shaft, or rotor speed is the product of turbine workapplied to a directly driven compressor. VNT turbine rotor speed can bealtered by tailoring the turbine's efficiency at the turbine wheel exitvia the exit configuration shape and size. The impact of the change inefficiency is used to match compressor and VNT characteristics to meetengine air system requirements. The sizing of the exit feature may belimited by resulting engine performance parameters in addition toturbomachinery speed control, i.e., fuel consumption or possibly enginepressure ratios.

By defining a shaped and sized step-bore in the turbine housing, at theturbine wheel exit, the turbine efficiency characteristic can beselectively tailored to improve turbine efficiency behavior, therebyenhancing VNT turbocharger EGR systems performance. Succinctly stated,the provision of a step-bore reduces the turbine efficiency, resultingin a favorable increase in turbine inlet pressure. The increased inletpressure promotes the flow of exhaust gas from the engine's exhaustmanifold into the engine's intake manifold. This beneficial turbochargerbehavior is accomplished, according to the invention, at a reducedturbocharger speed than would be attainable with a typicalturbomachinery turbine efficiency characteristic. Despite thecomparatively reduced turbocharger speed, performance is notcompromised; so the inventive apparatus may be fashioned from currentlyexisting production materials, and known processes for VNT turbochargersystems are applicable. Furthermore, lowered turbine efficiency providesthe capacity to drive a larger quantity of EGR flow into the engineintake manifold than would be possible with conventional turbine housingdesigns.

Attention is invited to FIG. 1, showing one embodiment of the apparatusof the invention. The turbine 10 features a turbine housing 12 that ismanufactured generally in accordance with the known art, except asfurther explained hereinafter. The turbine housing 12 substantiallysurrounds and defines a turbine bore 14 for receiving a turbine wheel(not shown in FIG. 1) rotatable upon a turbine shaft according generallyto convention. In one possible embodiment, the inlet side of the housing12 may be provided with a port 16 permitting the placement of theturbine wheel into the bore 14 during turbine assembly. After theinstallation of the turbine wheel, the port 16 is closed and secured by,for example, the bolted attachment of a turbocharger center housingrotating assembly (not shown).

With continued reference to FIG. 1, it is noted that the turbine housing12 features and defines a turbine tip diameter D_(TIP) that ordinarilycorresponds approximately to the maximum tip diameter of the turbinewheel, according with known art. Also defined is the turbine housingtrim diameter D_(TRIM)which varies among different turbine housingmodels, but corresponds generally to a functional diameter of theturbine wheel, there being a very close clearance between thecircumference of the wheel and the housing trim wall 17 defining thetrim diameter D_(TRIM). In some embodiments of the present invention,the turbine tip diameter D_(TIP) may be only slightly larger than thetrim diameter D_(TRIM).

“Downstream” within the bore 12 is the turbine diffuser or exducer 18, aconduit via which gas is exhausted from the turbine assembly. Thediameter D_(EX) is important in making an appropriate mechanical jointfor the coupling and size required for the exhaust system. Notably, theinvention has practical use in turbines employing generally cylindricalexducers, such as depicted in FIGS. 1, 4, 5, 6, and 8, as well asturbines having flared or conical exducers, such as those seen in FIGS.3 and 7.

Implementation of turbine efficiency tailoring is accomplished by, amongother things, affecting the gas flow into and through the exducer 18.Referring to FIG. 1, this may be achieved by the provision of a “step”in the bore 14, whereby the diameter of the exducer 18 is abruptlyreduced for an abbreviated portion of its axial length. For example, inthe embodiment of FIG. 1, there is provided a separately produced stepbore ring 20 that is insertable through the exducer 18 and into the bore14. As seen in FIGS. 2A and 2B, the step bore ring 20 is a rigid annulushaving an exterior diameter substantially equal to the exducer diameterD_(EX) so as to be snuggly received into the throat of the exducer 18,concentrically about the axis of the bore 14, as seen in FIG. 1. Thestep bore ring 20 may be there fixed in position by threaded bolts 21 orother suitable fastening means or integrated into the casting of theturbine housing.

Notably, the step bore ring 20 defines an aperture 22 therein,preferably concentric with the ring's outer circumference, having aselected tailored diameter d (FIGS. 2A and 2B). Tailored diameter d ispreferably and nearly always less than the exducer diameter D_(EX), andis smaller than the turbine housing trim diameter D_(TRIM). The stepdefined in the bore 14 by the step bore ring 20 thus is configured sothat the normal smooth flow of the gas exiting the turbine wheel isdisturbed, by constricted passage through the aperture 22 of the ring20, near the turbine wheel exit. The tailored diameter d is betweenabout 80 percent and 100 percent of the D_(TRIM). The precise ratiobetween d and D_(TRIM) is selected and determined to obtain the desiredtailoring. The ratio between the tailored diameter d and the housingtrim diameter D_(TRIM) affects the turbine efficiency characteristic.The performance tailoring of the turbine stage is associated with theimpact of the downstream orifice tailored diameter d on D_(TRIM) (inFIG. 1, for example).

The “step bore” resulting from the aperture 22 can be tailored such thatthe turbine efficiency can be matched to provide a similar efficiencycharacteristic to that which is desirable for VNT brand turbocharger EGRsystems

FIG. 9 is a graph showing relative impact of sizing of a fixedconfiguration d diameter with respect to a fixed trim diameter in termsof turbine pressure ratio and turbine efficiency. Modulating turbineefficiency via fixed d diameter sizing for a VNT turbine stage is ameans by which turbomachinery speed can be modified or matched to meet aspecific set of engine conditions. The efficiency impact of the orificediameter varies with size and operating pressure ratio. Performancecharacteristics of various configuration d diameter shapes will bevariable based on the basic shape of the orifice.

Reference is made to FIG. 3, illustrating a preferred embodiment of theinvention. The embodiment of FIG. 3 is very similar in many respects tothe embodiment of FIG. 1, except that the step bore ring 24 is cast inplace integrally with the housing 12. A turbine wheel 30 is shownmounted in the turbine bore 14. In this “fixed geometry” embodiment ofthe invention, a ring 24 cast integrally with the housing 12 providesthe step 25 in the bore. The ring 24 thus is a permanent extension ofthe cast housing, and is integrally associated therewith at the time ofhousing manufacture. This cast feature is generally annular, but moldedwithin the housing bore 14 as shown in the figure. The circular aperturein cast ring 24 defines the tailored diameter d. It is noted in FIG. 3that the exducer 18 is not cylindrical, but is a conical diffuser withan ever-increasing exducer diameter proceeding toward the turbineexhaust. The addition of the conical diffuser assists in fine-tuning thetailoring of the turbine performance.

In the embodiment of FIG. 3, the bore step feature is provided by thering 24 preferably cast integrally with the housing 12. Alternatively,the retainer ring 24 may be manufactured separately, and then insertedinto and secured within the turbine bore 14, as suggested by FIGS. 1, 2Aand 2B, and 4. The bore step 25 is defined by the edge of the aperturein the ring 24, which aperture has diameter d. The diameter d is thetailored diameter selected for turbine efficiency, and in any event isless than the trim diameter D_(TRIM). The turbine gases, of course, flowthrough the aperture in the ring 24, but the aperture is too small toadmit passage of the turbine wheel 30.

FIG. 5 illustrates how an insertable retainer ring 24, similar to theembodiment seen in FIG. 4, may offer apparatus adaptability. Aninsertable ring 24 may be disposed within the turbine bore and securedat one or more different axial locations. FIG. 5 shows the retainer ring24 secured (for example with bolts directed radially through the ringand into the housing) at an axially forward position. However, since theretainer ring 24 is removably insertable, its axial position also isselectively adjustable. As suggested by the phantom lines in FIG. 5, theretainer ring can be disengaged from an axially forward position,slipped to any second, rearward, location, and there again temporarilyfixed in place. This adjustment, which may be incrementally orinfinitely variable depending upon the mode of connecting the ring 24 tothe housing, permits the retainment and tailoring features of a singleturbine apparatus 10 to be customized to particular uses. By thisadjustability of the ring location, the axial position, and effect, ofthe reduced tailored diameter d defined by the ring can be regulated andselected for optimum turbine efficiency. The location of the retainerstep 25 likewise is adjustable (e.g., to accommodate a turbine wheel 30of different axial length).

The axial movement of the ring may be guided by two or morecircumferentially arrayed longitudinal guides 29, 29′, which may beintegral extensions of the housing 12 protruding from the turbine borewalls. Guides 29, 29′ also prevent radial shifting of the ring 24 aboutthe central axis of the apparatus. Removably insertable retainer rings24 can be removed and re-installed for maintenance or replacement.

Still another alternative embodiment of the invention is shown in FIGS.6 and 6A. Retainer and tailoring advantages are provided by a pluralityof profiled protrusions 33, 33′ cast integrally with the housing 12. Theprofiled protrusions could be variably rotated about an axis resultingin a variable tailoring of the turbine efficiency. The radial array ofconvex protrusions 33, 33′ extend radially inward into the throat of thebore 14, and preferably are uniformly spaced around the bore'scircumferential perimeter, as seen in FIG. 6A. As indicated in thefigures, especially FIG. 6A, effective tailored diameter d is definedapproximately by the average “height” of diametrically oppositeprotrusions. The protrusions 33, 33′ may have any of a variety ofprofiles or shapes. One preferred profile is depicted in FIGS. 6 and 6A,where each protrusion has a somewhat oval or “tear drop” footprint andan airfoil axial profile. Any of wide variety of shapes and profiles aresuitable to the function of the invention, although smooth, aerodynamicprofiles such as those seen in the figures are preferred.

Alternatively, the protrusions 33, 33′ may be more rectilinear orvane-like in form than those shown. FIGS. 7 and 7A depict an alternativeembodiment with a plurality of uniformly spaced rectilinear protrusions33, 33′ (eight protrusions in the embodiment of FIGS. 7 and 7A.) As seenin the figures, the protrusions may have, for example, a low axialprofile, each protrusion 33 featuring a quadrilateral axial section witha leading “face” perpendicular to the turbine axis, and a trailing facedefined by an acute angle that allows the trailing face to mergesmoothly into the inside wall of the exducer 18. Again, the effectivetailored diameter d is determined using the approximate average radialextension of the protrusions.

In any embodiment featuring an arrayed plurality of protrusions 33, 33′,the longitudinal axes of the protrusions, while preferably beingmutually parallel, may be canted or angled in relation to the axis ofthe turbine, to foster “de-swirling” of the exhaust gas as it exits theturbine wheel 30. The number of protrusions 33, 33′ also is selectable,and may number, for example, between three and eight (eight in theembodiments of FIGS. 6 and 7).

Yet another embodiment of the invention is shown in FIGS. 8 and 8A. Thisembodiment of the invention permits the use of an adjustable bore stepwithin a conical, as opposed to cylindrical, exducer. In thisembodiment, a segmented ring 27 has a variable diameter, so as to expandor contract according to need corresponding to the oblique annular faceof the conical exducer 18. The ring segments 31, 31′ can vary in number,the plurality numbering at least three (four shown in FIGS. 8 and 8A)and up, for example, eight or ten.

The embodiment of FIGS. 8 and 8A thus shares some of the features andadvantages of the embodiments seen in FIG. 5, except that in addition tobeing selectively adjustable in axial position within the housing 12,the effective diameter of the step ring 27 can be adjusted, as can theeffective tailored diameter d defined by the aperture in the ring 27. Toincrease the tailored diameter d, the uniformly spaced segments 31, 31′are shifted radially outward, thus increasing the size ofcircumferential gaps that separate adjacent segments. Likewise, when thering 27 is moved to a forward position in the exducer, the diameter d isreduced by reducing the gaps between adjacent segments of the ring 27.

The ring segments 31, 31′ manifest wedge-shaped longitudinal profiles,as seen in FIG. 8A, and thus can shift simultaneously axially andradially by riding along the annular chamfer 35 in the bore. The ringsegments are arrayed so as to always define a segmented annulus, andsecured at one or more different axial locations. FIG. 8 shows thesegments of the retainer ring 27 secured (for example with boltsdirected radially through the ring and into the housing) at an axiallyforward position. However, since the retainer ring 27 is movablyinsertable, its axial position also is selectively adjustable. Assuggested by the phantom lines in FIG. 8, the retainer ring 27 can bedisengaged from an axially forward position, slipped to any second,rearward, location, and there again temporarily fixed in place. Due tothe changed diameter of the exducer 18 in which the ring 27 is disposed,the ring 27 tailored diameter d likewise is modified. This adjustmentpermits the retainment and tailoring features of a single turbineapparatus 10 to be customized to particular uses. By this adjustabilityof the ring location, the axial position and size, and effect, of thereduced tailored diameter d defined by the ring can be regulated andselected for optimum turbine efficiency. The location of the retainerstep 25 likewise is adjustable (e.g., to accommodate a turbine wheel 30of different axial length).

As with the embodiment of FIG. 5, the axial movement of the ring 27 maybe guided by two or more circumferentially arrayed longitudinal guides(not shown in FIG. 8) which may be integral extensions of the housing 12protruding from the turbine bore walls.

The apparatus of the invention provides, therefore, a step bore 25 inall embodiments that serves to retain the turbine wheel 30 againstimproper displacement toward the rear of the turbine housing 12. Theretainer, typically an annular ring with or without customizedprotrusions, permits a tailored diameter d in relation to the trimdiameter T_(TRIM) to optimize the turbine efficiency characteristic.

By designing, shaping and sizing a “step bore” in the turbine housing,near the turbine wheel exit, the turbine efficiency characteristic canbe modified or tailored, resulting in a turbine efficiency behaviorwhich is more favorable to the performance of the variable nozzleturbine turbocharger EGR system according to the present invention. Ineffect, the step bore 25 reduces the turbine efficiency, which resultsin an increased turbine inlet pressure, which promotes the flow ofexhaust gas from the engine's exhaust manifold into the engine intakemanifold. This behavior is accomplished at a lower turbocharger speedthan would be achievable with an ordinary turbomachinery turbineefficiency characteristic.

Although the invention has been described in detail with particularreference to these preferred embodiments, other embodiments can achievethe same results. Variations and modifications of the present inventionwill be obvious to those skilled in the art and it is intended to coverin the appended claims all such modifications and equivalents. Theentire disclosures of all references, applications, patents, andpublications cited above are hereby incorporated by reference.

What is claimed is:
 1. A turbine apparatus comprising: a turbine housingpartially enclosing an axial bore and axial exducer, said bore having atrim diameter; a turbine wheel rotatably mounted within said bore; and aretainer disposed in said exducer proximate to said turbine wheel, saidretainer defining a bore step and an aperture therein having a tailoreddiameter; wherein said trim diameter exceeds said tailored diameter. 2.An apparatus according to claim 1 wherein said tailored diametercomprises from about 80 percent to about 100 percent of said trimdiameter.
 3. An apparatus according to claim 1 wherein said retainercomprises an annular ring.
 4. An apparatus according to claim 3 whereinsaid ring is cast integrally with said housing.
 5. An apparatusaccording to claim 3 wherein said ring is removably insertable into saidexducer.
 6. An apparatus according to claim 5 wherein said ring isselectively positionable longitudinally and securable along the axis ofsaid exducer.
 7. An apparatus according to claim 6 wherein said ringcomprises a plurality of ring segments movable radially in relation tothe axis of said exducer.
 8. An apparatus according to claim 3 whereinsaid ring further comprises a plurality of protrusions extendingradially inward in relation to the axis of said exducer.
 9. An apparatusaccording to claim 8 wherein said protrusions are mutually parallel anddisposed obliquely in relation to the axis of said exducer to promotede-swirling of turbine exhaust.